1. Field of the Invention
This invention is in the field of electrical motor structures and, particularly the field of alternating-current motor structures having induction-type rotors.
2. Description of the Prior Art
Prior-art induction motors are, in commercially successful form, constructed with cylindrical rotors and stators in which hollow, cylindrical, laminated, magnetic cores of the stators surround the cylindrical, laminated, magnetic portions of the rotors. The laminated portions of the rotors typically have squirrel-cage arrays of conductors formed in slots on the outer cylindrical surfaces of the rotors and on the end circumferences of the rotors.
The magnetic fields of conventional induction motors are associated with phased alternating currents and voltages applied to the stators and with phased alternating currents and voltages induced in the rotors as the rotational velocities of the rotors slip with respect to the rotating stator fields. The time-varying magnetic fields associated with the stator and rotor windings typically enter and leave at separate locations both on the inner surface of the laminated stator core and on the outer surface of the laminated rotor, requiring field paths having tangential direction within each of those laminated structures. Therefore, each of the laminated structures must have a radial thickness of sufficient dimension that the combined stator and rotor magnetic flux densities do not saturate while moving in tangential paths within those structures.
Prior-art structures, in general, have limited electromechanical energy transfer capability at high frequencies. One reason for that loss of capability is the inability to compensate for leakage inductance associated with the alternating-current windings.
Hysteresis losses in the laminated prior-art structures, particularly the stator cores, are relatively large because the combined rotor and stator magnetic fields reverse direction at every point in the laminated structures with each cycle of alternating-current and corresponding rotation of the rotors. The hysteresis losses per unit volume would be decreased if the magnetic fields at each point in the stators and rotors did not reverse directions, but varied in only one direction between a minimum value and a maximum value during each cycle, thus avoiding operation involving the major hysteresis loops of the laminated magnetic materials.
Conventional induction motors operate at power factors that are less than ideal. Correction to improve those power factors is accomplished through use of external circuitry and devices that do not minimize the magnitude of current in the stator windings of the machines.